Conventionally, there is known a sheet processing apparatus in which a plurality of sheets conveyed from an image forming apparatus, such as a copying machine, a multi-function peripheral or the like, are loaded up on a processing tray into a sheet bundle and then a post-processing, such as stapling and sorting, is applied on the sheet bundle. Such a sheet processing apparatus is configured to shift the sheet bundle on the processing tray in a width direction orthogonal to the sheet conveying direction so as to position the sheet bundle at a stapling position or to sort the sheet bundle. The processed sheet bundle is discharged on a stacking tray by a discharge part composed of an upper and lower roller pair.
In such a sheet processing apparatus, while the processed sheet bundle is stacked on the stacking tray, a previously discharged sheet bundle may be pushed by a leading end of a newly discharged sheet bundle and then be dislocated on the stacking tray or drop from the stacking tray.
As a countermeasure on this problem, Patent Document 1 discloses a sheet processing apparatus including a pressing member pressing a rear end of the discharged sheet bundle on the stacking tray.